What is my PC Capable of Doing in Blender?
Well, First of all, your PC is perfectly fine for learning Blender. You can do everything and anything with it.

Even an EEEPC with 2x1.6 ghz and 2GB ram is enough to do that. You might want to run it under Linux but that's not a problem.

You can test the performance easily. Just make a cube with 10k faces and duplicate it until rotating gets sluggish. Sluggish means: stay below that. You'll find your threshold in the upper right. You can also hit SPACE and type redraw timer. That'll tell you how long Blender takes to redraw the screen with its current content.

Rendering: also, just make test scenes and find the stuff you still find bearable.

There's cool low poly stuff out there. Blender is also very cool for cutout animation. Check Monty Python and Terry Gilliam for that (well, or South Park). Watch a game walkthrough like Limbo, check a movie like Renaissance and you can see that it doesn't take fancy lighting, 50 million polygons and lots of reflections to create atmosphere. ASDFmovie is very successfull, too. 

You could do a full 90 minute movie with your machine and the rendering wouldn't be excessively long as long as you don't try to do Pixar and know enough tricks. If the story is great and the acting is decent and the camera work is good, simplified visuals can even be a strength. 

If you are frustrated with your PC being small, you are actually frustrated with your current income. The PC is only a symptom. That would be subject to strategic planning and lots of learning and practicing and daily focus on a course that financially makes sense and is sustainable.